This invention relates to a graphic display system for use in computer graphics.
In a conventional graphic display system, a segment buffer for display lists is provided in a data memory unit in a graphic controller 22 as shown in FIG. 2. The display lists stored in the segment buffer 21 of the data memory unit are prepared by processes which are executed by a central processing unit 14. These display lists are read out and processed by the graphic display controller 22 and graphics are displayed on a monitor 13 based on the display lists.
The process to be executed by the central processing unit 14 is executed in the following way. Data of the original of the graphic image to be displayed are stored in the main memory 16 as a part of, for example, a CAD data base. In general, the graphic display controller cannot use directly the original data. Therefore, the central processing unit 14 accesses the data with process addresses through memory management unit 15 in order to convert them to the display lists that can be used by the graphic display controller 22. The display lists are then stored in the segment buffer 21 contained in the graphic display controller 22 through the memory management unit 15. Thereafter, the graphic display controller 22 accesses the display lists stored in the segment buffer 21 with graphic addresses and displays the graphic image on the monitor 13. Therefore, the copying and moving of data occurs a large number of times and also data conversion processing performed by the central processing unit 14 is necessarily required even when a part of the original data can be used directly by the graphic controller. As a result, the processing speed of the graphic display system is slow.
A sufficiently large segment buffer 21 is necessary in order to store the display lists and this results in increased costs of production. Moreover, the segment buffer memory area in the graphic controller 22 is used solely for holding the display lists and cannot be used as the memory area for other purposes. On the other hand, the segment buffer 21 in the graphic display controller 22 has a limited memory capacity, and display lists exceeding this memory capacity cannot be stored.
The memory area accessed in the process to be executed by the central processing unit 14 is determined through the mapping from the logical address of the process to the physical address of the main memory 16 by the memory management unit 15 and is prepared in the main memory 16. For this reason, the graphic display controller cannot determine the physical address of the data stored in the main memory and therefore cannot access directly the data in the process even when data can be used directly by the graphic display controller.